The prior art discloses height-adjustable vehicle seats in which a belt buckle is co-moving, that is to say participates in the movement of the height adjuster in order, for example, in the case of a belt retractor which is blocked because of an abrupt movement and subsequent electric adjustment of the seat height upward, to avoid an uncomfortably high force between belt and occupant. Since the belt buckle of the vehicle seat is generally arranged on the inner side of the vehicle (tunnel side), but the geared motor required for an electric adjustment can customarily not be placed on the tunnel side for construction space reasons, the force introduced into the height adjuster by the belt buckle is transmitted over the entire rigidity of a substructure of the vehicle seat from the tunnel side onto the outer side of the vehicle (sill side) and absorbed there by a geared motor which is configured to be self-locking. Due to these spatial conditions and the rigidity of only a finite magnitude of the vehicle seat components located in the force flux, during an introduction of load via the belt into the belt buckle, a significant travel of the belt buckle is produced in the load direction, which travel, under some circumstances, results in an undesirably great movement of the occupant relative to the rest of the vehicle interior. In order to solve this problem, what are referred to as crash blocking units are known from the prior art, said crash blocking units being installed on the tunnel side of the seat, i.e. in the direct vicinity of the belt buckle, and, in the event of loading of the belt buckle, providing an additional stiff connection within height adjuster kinematics. Said crash blocking units generally block the rotational movement between a seat rail and rear rocker, coupled to the seat rail, of the height adjuster kinematics.
A corresponding crash blocking unit is known from WO 2004/074037 A1. An insertion movement, which is forced kinematically under a crash loading, of a pawl coupled to a rear rocker into the toothing of a tooth segment connected to the seat rail causes a blocking of the rotational movement between the rear rocker and the seat rail as a function of the load. Although the crash blocking unit according to WO 2004/074037 A1 significantly reduces the travel occurring upon loading of the belt buckle with a high force, in the event of particularly soft seat substructures a necessary deformation of the vehicle seat that is required for triggering the crash blocking unit can be quite high, particularly since the loadings which occur during the normal driving mode can lead to elastic deformations which, however, are not yet intended to allow the crash blocking unit to be triggered. In order to suppress triggering under use loads, the triggering threshold of the crash blocking unit has to be selected to be appropriately high, but this results in a later engagement in the event of a crash and therefore in an undesirably large relative movement of the belt buckle.
DE 100 56 082 B4 discloses a solution in which a system which blocks as a function of deceleration can be additionally activated as a function of load. A belt connection point is mounted movably, and a relative movement, which arises under loading, between the belt connection point and a seat frame is transmitted by means of a cable to a catch fixed on the seat rail.